A power and free conveyor of the type above described is shown in U.S. Pat. No. 3,503,337. A problem has been found to exist during stopping of the carriers in that when a carrier is suddenly arrested by engagement of the stop member with the stop lug on the carrier body, the carrier tends to rebound back away from the stop member and this rebound is sometimes sufficient to allow the pusher dog to be released by the stop member, whereby the next depending pusher lug on the conveyor chain will re-engage the pusher dog once more, propelling the carrier forward and into engagement with the stop member. Thus, a serious bump-and-release-bump-and-release sequence may be initiated which is potentially damaging to the entire conveyor system as it can cause breakage of lugs, dogs, stops, etc. necessitating shutdown of the conveyor system.
Another prior art U.S. Pat. No. 3,437,054 provides a hold-back dog spaced rearwardly of the pusher dog which is intended to engage the stop member and arrest movement of the carrier. However, this structure requires that the main track and the conveyor chain track be spaced vertically farther apart at the stop stations to avoid engagement of the pusher lug with the hold-back dog.
In U.S. Pat. No. 3,434,431 the hold-back dog is pivoted on the carrier. I have found this unreliable and noisy during accumulation and on downgrades, respectively.
Accordingly I have discovered that both the rebound problem raised by U.S. Pat. No. 3,503,337 and the problems of the structure shown in U.S. Pat. Nos. 3,437,054 and 3,434,431 may be obviated. My solution is particularly, though not exclusively, appropriate for use with power and free carriers wherein the hold-back dog is enslaved to the pusher dog such that when the latter is depressed by the stop member or otherwise, the hold-back dog is also depressed.